1. Field of the Invention
The present invention relates to a novel polyurethane, to a process for its production and also to a polyester diol used for its production.
2. Description of the Related Art
Polyurethanes have various features such as high elasticity, high abrasion resistance, high resistance to oil and the like, and have hence caught much attention as substitutes for rubber and plastics. Thus, polyurethanes have widely and in large amounts been used as molding materials which are moldable by conventional plastic molding processes. Polyurethanes are produced by mixing and polymerizing a high polymer diol, a diisocyanate and a chain extender such as 1,4-butanediol. It is known to be preferable to melt starting materials, and mix and polymerize them.
Known polyurethanes are classified into polyester-, polyether- and polycarbonate-based ones, and they are used for various items according to their specific features. For instance, polyether-based polyurethanes are used in fields where resistance to hydrolysis is particularly required; polyester-based ones in fields where high mechanical properties and resistances to oil and abrasion are particularly required; and polycarbonate-based ones in fields where high durability is required in addition to the requirements as satisfied by polyester-based polyurethanes.
Among polyester-based polyurethanes, poly(butyleneadipate)-based ones, poly(hexamethyleneadipate)-based ones and the like are widely used because of their availability and, in general, relatively high performances. However, these widely used polyester-based polyurethanes often do not satisfy requirements from processability and from finished product properties, since they have low resistances to heat, water and cold and have some problems in injection moldability such as long cycle time, which cause productivity to decrease, generation of sink marks and the like. There have therefore been strongly desired improvements for the above drawbacks.
As polyester-based polyurethanes improved in resistances to water and cold, European Patent Application Publication No. 194452 and U.S. Pat. No. 4,639,471 disclose one prepared from, as the high polymer diol, a polyester diol obtainable by reacting 1,9-nonanediol, a specific diol having a methyl branch, such as 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol or neopentyl glycol and a dicarboxylic acid. For the same purpose European Patent Application publication No. 299068 discloses one obtainable by utilizing as the high polymer polyol a polyester polyol obtained by reacting 2-methyl-1,8-octanediol or its mixture with a linear alkylene glycol having 6 to 9 carbon atoms with a dicarboxylic acid. The above European Patent Application publication No. 194452 and U.S. Pat. No 4,639,471 describe that ethylene glycol, propylene glycol or 1,4-butanediol can, in the production of the polyester polyol, be added to a mixture of 1,9-nonanediol and a diol having a methyl branch, provided that the amount added does not exceeds 5% by weight based on the weight of the mixture. Further the above European Patent Application Publication No. 299068 describes that a great decrease in resistance to hydrolysis and flexibility at low temperatures is observed in polyester-based polyurethanes produced by utilizing a polyester polyol obtained by reacting a dicarboxylic acid with a diol having not more than 5 carbon atoms, instead of the linear alkylene glycol having 6 to 9 carbon atoms, together With 2-methyl-1,8-octanediol. The present inventors have found that the above-proposed two types of polyester-based polyurethanes having improved resistances to water and cold often show a markedly improved injection moldability but are still of not sufficiently improved heat resistance.